Sodium dithionite solution stabilization

ABSTRACT

Sodium dithionite in solution is widely used in bleaching and vat dyeing of textiles. Unfortunately, however, losses occur not only through decomposition during dissolving of the salt in question, but also during storage of the solution. To avoid decomposition of such solutions, the presence of sulfite ion is introduced by sodium sulfite, or a comparable variant compound preferably with a pH adjustment under either aerobic or anaerobic conditions. The effect hereof in protecting the sodium dithionite against aerobic decomposition is at 7 percent to 45 percent of the decomposition rate for unprotected systems. With air exclusion, the rate in the protected system is at 2 percent to 71 percent that for the unprotected system. As indicated, mixtures of sodium sulfite or sodium bicarbonate with sodium bisulfite (anhydrous) have likewise been found effective as a stabilizing media for the sodium dithionite solution, all by virtue of the sulfite ion concentration increase therein.

United States Patent 1 Kise et al.

[ Nov. 20, 1973 SODIUM DITHIONITE SOLUTION STABILIZATION [75] Inventors: Mearl A. Kise, Portsmouth; Leonard C. Ellis, Chesapeake, both of Va.

[73] Assignee: Virginia Chemicals Inc.,

Portsmouth, Va.

[22] Filed: Jan. 14, 1972 [21] Appl. No.: 218,011

Related US. Application Data [63] Continuation-impart of Ser. No. 3,527, Jan. 16,

1970, abandoned.

[52] US. Cl 252/188, 252/105, 8/110, 423/515 [51] Int. Cl C0lb 17/66 [58] Field of Search 252/188, 105; 8/110; 423/515 [56] References Cited UNITED STATES PATENTS 3,183,191 5/1965 Hach 252/188 1,736,464 11/1929 Rodman et a1. 252/188 2,995,522 8/1961 Joyce 423/515 OTHER PUBLICATIONS Chemical Abstracts, American Chemical Society, Vol. 73, 1970, l2l490a.

Primary Examiner-Leon D. Rosdol Assistant Examinerlrwin Gluck Attorney-J. Gibson Semmes [5 7] ABSTRACT Sodium dithionite in solution is widely used in bleaching and vat dyeing of textiles. Unfortunately, however, losses occur not only through decomposition during dissolving of the salt in question but also during storage of the solution. To avoid decomposition of such' solutions, the presence of sulfite ion is introduced by sodium sulfite, or a comparable variant compound 11 Claims, No Drawings SODIUM DITHIONITE SOLUTION STABILIZATION CROSS REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION M. Wayman, C.B. Anderson, W. J. Lem and W.H.

Rapson, Tappi, 52 (1), 89-92 (1969) Joyce US. Pat. No. 2,995,522

Hach US. Pat. No. 3,183,191

SUMMARY OF THE INVENTION Under either an aerobic or anaerobic condition, low concentration sodium dithionite solutions treated with small but effective amounts of sodium sulfite or sodium bicarbonate with sodium bisulfite (anhydrous) tend to effect a sulfite ion concentration and with initial and sequential pH adjustment, the reaction effects a stabilization of sodium dithionite in aqueous solution. The conditions surrounding the intended stabilization reac- Although the product sodium dithionite under norl5 ti on will be described hereinafter.

mal storage conditions, moisture being excluded and free circulation of air avoided, can be held without appreciable decomposition for several years, upon dissolution of the product in water, decomposition takes place immediately. To avoid this degradation in solution and to prevent acceleration thereof to total decomposition is a problem that has plagued the industry for years. Known decomposition reactions of this valuable commercial bleaching compound are as follows, depending upon the acidic environment wherein the stronger the acidic condition the faster the rate of reaction.

ANAEROBIC REACTION 25 0, H O 8 0'} ZHSOI,

AEROBIC REACTION 0", H O 0 HSO' HSO] would not appear to be a serious factor in large storage 4 systems the depth of oxygen penetrating through the surface of the storage system is not great in comparison to the entire depth auto-oxidation by anaerobic decomposition is inevitable regardless of solution depth or volume, per se.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Aerobic Stabilization I To achieve the stabilizing effect on a 5 percent aqueous solution of sodium dithionite for example, sodium sulfite or sodium bisulfite (anhydrous) was introduced under aerobic conditions at 31 Centigrade to 32 Centigrade. The results appear on Table I indicating that under this influence of the sulfite ion, the decomposition rate for such a stabilized aqueous solution is at 7 percent to 45 percent of that for an unprotected dithionite solution stored under comparable conditions. Reference compartive Run 718-65 (unprotected) and 718-97, the pH was adjusted to an initial value of 6.0. It will be observed that upon the introduction of less than half of one percent of the sodium sulfite to a 5 percent aqueous solution of sodium dithionite, the percentage of decomposition is drastically reduced over a comparable period of time.

With respect to the addition of a' sodium bisulfite (anhydrous) (Run 718-125) under comparable conditions, a marked diminution in the percentage of com- 0 position for a comparable period of time is shown. But

as the strength of the sodium bisulflte solution is increased, to compensate for a substantially stronger sodium dithionite aqueous solution (15 percent), a marked diminution in the percentage of decomposition is shown. (Run 718-133) TABLE I I Aerobic decomposition of sodium dithionite in presence of sodium sulfite and sodium bisuliite (anhydrous) Percent Percent pH Temp Time, Decomp./ Run number nazszo, NazSO; N aHSO range min. Decomp. min.

1n the past, the solution has been stabilized to a degree by treatment with caustic or ammonia. Cadmium sulfate as a stabilizer for sodium dithionite prepared in situ from sodium borohydride and sodium metabisulfite is another known form of stabilization. But the adverse effect in bleaching will be obvious from an examination of the reaction formula to yeild yellow cadmium sulfide, a distinct deterrent to brightness in a commercial bleaching operation, per se.

Known references in the literature include the following:

Chemical Week, July 27, 1968, pp. 54-55 Anaerobic Stabilization I] With respect to the anaerobic'study in Table II, in Runs 717-63 and 717-79, the initial pH was set at 6.1 to 6.2. Here the dithionite system, stabilized by sodium sulfite (Run 717-79) decomposed at only 20 percent of the rate of the unprotected solution, (Run 717-63).

Without initial pH adjustment, in systems containing 5.8 percent to 10 sodium sulfite based on the dithionite content, it was found that the decomposition rate of the protected system was 2 percent to 71 percent of that for the unprotected system. Reference Runs Nos.

TABLE 11 anaerobic solution stability in the presence of mixtures of sodium bicarbonate and sodium bisulfite (anhydrous), similar results to those achieved through Table 111 were noted. This is the sodium bicarbonate sodium bisulfite (anhydrous) system wherein increased concentrations of the additives. essentially an increase also in the sulfite ion concentration, yielded increased stability of the sodium dithionite, the pH ranges being generally established uniformly at 6. The most significant runs are Nos. 697-231 and 697-229.

Anaerobic decomposition of sodium dithionite in presence 01 sodium sulfite and sodium disulfite (anhydrous) Percent Percent pH Temp. Time, Decomp./ Run number Na SzO NazSO NaHSOi range C min. Decomp. min.

. 1-5. 5 50. 0 90 53. 7 0. 0o 2-5. 7 50.0 90 10. 1 0. 11 .5-54 50.0 00 46.8 0.52 .as.1 50.0 02 34.1 0.37 2-7. 0 50. 0 00 3. 8 0. 04 .86.1 50.0 01 34.1 0.38 .84.7 50.0 81 34.2 0. 42 -5.5 51.5 90 22.9 0.25 32. 0 30. 7 1. 02 51.0 00 33.4 0. 37 10.0 71 40.0 0.50 10.0 71 84.3 1.10

Anaerobic Sta ilizati n l l Sulfite ion per se shall be deemed herein to include Table 111 is illustrative ofa system of establishing anathat which is derived from reaction of either sodium erobic solution stability in the presence ofa mixture of lf te or sodium bisulfite (anhydrous) with the aquesodium sulfite and sodium bisulfite (anhydrous), the ous solution of sodium dithionite. sodium dithionite being an approximate 5 percent solu- Test Procedure tion. Here it is noteworthy that the decomposition rate The following steps outline the procedure employed of the sodium dithionite solution decreases from 0.55 in preparing the sodium dithionite solutions for decompercent per minute to 0.10 percent per minute, as the position studies under aerobic and anaerobic condiindividual compositions are raised from 0.025 percent tions. by weight in the solution to 0.20 percent. 1. A sealed plastic glove bag was loaded with nec- The stability of the solution increased significantly essary supplies and evacuated. The bag was then although the pH remained essentially the same. Even in twice filled with nitrogen and re-evacuated. A final Run 718-187 where the ratio of bisulfite ion to sulfite fill was m with high puri y nitr g n 2 ppm ion was increased greatly and there was a definite low- 40 02) to minimize d mposition by oxygen during ering of the pH to a point very near the critical region for rapid decomposition, the decomposition rate was only 20 percent of that for the unprotected system.

TABLE III solution preparation. 2. The desired amount of deaerated water was measured in a graduated cylinder and transferred to a Sodium dithionite-anaerobic solution stability in presence of various mixtures of sodium sulfite and sodium bisulfite (anhydrous) Percent Percent pH Temp. Tim Decomp./ Run number NazSz01 NazSO; NaHSO3 range C. min. Decomp. min.

Anaerobic Stabilization lV With respect to Table IV in which there is illustrated TABLE IV Z-Iiter aspirator bottle. The sulfite additive to be evaluated was charged, with agitation, to a certain Sodium dithionite-anaerobic solution stability in presence of various mixtures of sodium bicarbonate and sodium bisulfite (anhydrous) Percent Percent pH Temp. Time, DecompJ Run number NflzszO NaiSO; NaHSOa range C. min. Decomp. min.

718-245 5. 0 r 6. 5-5. 4 50. O 90 46. 8 0. 52 718-137 5.0 0. 016 0. 076 6. 1-5. 5 50. 5 46. 2 O. 51 5.0 0. 033 0. 156 5. 7-5. 4 50. 0 81 32. 5 0. 40

5. (l 0. 050 l). 235 6. 4-6. 2 49. 1) 8O 21. 7 0. 27

weight percentage of the total solution. Agitation was continued until solution of the additive was complete or for a maximum of 5 minutes. For tests in which the initial pH was adjusted to 6.0, 0.3percent NaOH was dissolved in the water before addition of the additive. After transfer of the dithionite mixture to the test vessel, 2percent H 80 was added for adjustment of pH to 6.0.

3. Sodium dithionite was then added with strong agitation to the additive-water solution. The time was measured from first contact of sodium dithionite with the aqueous mixture. Time in the aerobic studies was measured at the start of the air flow through the test mixture. Agitation was continued for a total of four minutes at which time sufficient mineral oil was added to cover the surface.

4. During time required to carry out steps 1-3, a 2- liter glass resin reactor, fitted with an agitator, pH probes and sufficient inlets and outlets to allow sparging and addition of solution under anaerobic conditions, was placed in a constant temperature bath at 50C and sparged with high purity nitrogen for a minimum of minutes. Aerobic studies were made herein at 30C; air flow was controlled by a rotameter which had been calibrated with a wet test meter; air addition was begun when the reaction mixture reached 30C.

5. After sparging, the reaction mixture, exluding the layer of mineral oil, was charged to the test reactor. Periodic readings of pH and temperature were taken in conjunction with samples. The samples were titrated for dithionite content with rubine and titanous chloride.

In Step 2 of the foregoing Test Procedure, the addition of the sulfite additives was found to buffer the solution by an "alkaline reserve" process. Thus, when the sulfite stabilizers have been added to the solution, the pH factor was found to be additionally controlled by these stabilizers, preventing the solution from becoming too acidic with the undesirable result of dithionite decomposition. The adjustment of the pH to approximately 6.0 after the transfer of dithionite was further achieved by the addition of hydrogen sulfate, as described in the Test Procedure. Thus, the pH of the sodium dithionite solution was ultimately contained within the range of 4.0 to 7.2 over the test period using the bisulfite additives, as reported above.

We claim:

1. A method to stabilize aqueous solutions of sodium dithionite falling within the low concentration range of 6 4.6 percent to 15.0percent during preparation and storage thereof comprising the steps of:

A. initially establishing the pH factor in the said solution at from 5.0 to 8.0; and

B. sequentially increasing by reaction the concentration of the sulfite ion in the sodium dithionite solution by adding at least one sulfite ion containing compound of not greater than 1.0 percent strength, whereby an alkaline reserve in the solution is created to effect continuous control of the pH within the range of from 5.0 to 8.0.

2. The method according to claim 1, wherein the concentration of the sulfite ion is effected by the addition of sodium sulfite in a small but effective amount not to exceed 1.0 percent strength.

3. The method according to claim 1, wherein the concentration of the sulfite ion is effected by the addition of anhydrous sodium bisulfite in a small but effective amount.

4. The method according to claim 1, wherein the concentration of the sulfite ion is effected by the addition of a mixture of sodium sulfite and anhydrous sodium bisulfite in a small but effective amount.

5. The method according to claim 1, wherein the concentration of the sulfite ion is effected by the addition of a mixture of sodium bicarbonate and anhydrous sodium bisulfite in a small but effective amount not to exceed 1.0 percent.

6. The method according to claim 1, wherein the increased concentration is effected by simultaneous admixture and agitation of a sulfite ion additive with the sodium dithionite, the proportion of additive to solution being a small but effective amount.

7. A reaction product for bleaching including a low concentration aqueous solution of sodium dithionite, falling within the range of 4.6 percent to 15 percent and a sulfite ion additive having a concentration not to exceed the extreme of 1.0 percent.

8. The product of claim 7 in which the additive comprises sodium sulfite.

9. The product of claim 7 in which the additive comprises anhydrous sodium bisulfite.

10. The product of claim 7 in which the additive comprises sodium sulfite and anhydrous sodium bisulfite in admixture.

11. The product of claim 7 in which the additive comprises sodium bicarbonate and anhydrous sodium bisulfite not to exceed in admixture 1.0 percent. 

2. The method according to claim 1, wherein the concentration of the sulfite ion is effected by the addition of sodium sulfite in a small but effective amount not to exceed 1.0 percent strength.
 3. The method according to claim 1, wherein the concentration of the sulfite ion is effected by the addition of anhydrous sodium bisulfite in a small but effective amount.
 4. The method according to claim 1, wherein the concentration of the sulfite ion is effected by the addition of a mixture of sodium sulfite and anhydrous sodium bisulfite in a small but effective amount.
 5. The method according to claim 1, wherein the concentration of the sulfite ion is effected by the addition of a mixture of sodium bicarbonate and anhydrous sodium bisulfite in a small but effective amount not to exceed 1.0 percent.
 6. The method according to claim 1, wherein the increased concentration is effected by simultaneous admixture and agitation of a sulfite ion additive with the sodium dithionite, the proportion of additive to solution being a small but effective amount.
 7. A reaction product for bleaching including a low concentration aqueous solution of sodium dithionite, falling within the range of 4.6 percent to 15 percent and a sulfite ion additive having a concentration not to exceed the extreme of 1.0 percent.
 8. The product of claim 7 in which the additive comprises sodium sulfite.
 9. The product of claim 7 in which the additive comprises anhydrous sodium bisulfite.
 10. The product of claim 7 in which the additive comprises sodium sulfite and anhydrous sodium bisulfite in admixture.
 11. The product of claim 7 in which the additive comprises sodium bicarbonate and anhydrous sodium bisulfite not to exceed in admixture 1.0 percent. 